How your laptop finds the computer behind "wikipedia.org"
Packets need an IP address, but you typed a name. DNS (the Domain Name System) is the worldwide directory that turns a name like wikipedia.org into an address like 185.15.59.224, which your computer then puts on its packets.
The directory is split by the dots, read from the right. Root servers know who runs each top-level domain (TLD) like .org; the .org servers know who runs wikipedia.org; its authoritative server, run by its owner, holds the record.
A record is one typed entry: an A record holds an IPv4 address, AAAA an IPv6 one. Queries usually go in one small UDP packet to port 53, with no TCP handshake, so each server asked costs one round trip.
How the internet works · 4 of 102 / 3
DNS
Real-life use case
Twitter went dark in 2016 while its servers kept running
In October 2016 a botnet (a network of hijacked devices) flooded Dyn, which ran DNS for Twitter, Netflix and Reddit. Their servers were fine, but many resolvers couldn't get their addresses, so the sites seemed down.
Your device sends lookups to a recursive resolver, a server that chases answers for you, usually your internet provider's. In Wi‑Fi settings you can swap in Cloudflare's 1.1.1.1 or Google's 8.8.8.8.
If your resolver fails, the internet itself still works but names don't, and Chrome shows an error starting with DNS_PROBE_FINISHED.
How the internet works · 4 of 103 / 3
DNS
How it helps
Your resolver remembers answers, so most lookups take one question
On a first lookup the resolver walks down the tree: the root points to the .org servers, they point to wikipedia.org's server, which gives the address. Each server only hands over the next pointer, so none must know everything.
Every answer carries a TTL (time to live): how many seconds it may be cached. Until then, the next person asking gets it in one round trip. But after a site moves, some users get the old address until the TTL runs out.
Pointers are cached too: once the resolver knows the .org servers, it skips the root for every .org name. That is why the root servers, 13 named addresses (a to m) copied across many sites worldwide, are rarely asked anything.
What it’s forEstimates how long turning a name into an address takes.
lookup time ≈ RTT_resolver + (RTT_root + RTT_TLD + RTT_auth, only for steps not cached)
RTT_resolver
round-trip time from your device to its resolver, e.g. 10 ms
RTT_root
round trip from the resolver to a root server
RTT_TLD
round trip to the top-level domain servers, e.g. for .org
RTT_auth
round trip to the domain's own authoritative server
What it givesThe delay before your browser can even start connecting, from a few ms when cached to around 100 ms when not.